Together with the increase in integration of semiconductor devices, the circuit width line required for the semiconductor devices has grown smaller year by year. In order to form a desired circuit pattern on a semiconductor device, a high-precision original image pattern is required. Accordingly, the electron beam lithography technique has inherently excellent resolution, and is used for production of original patterns with a high degree of accuracy.
FIG. 6 is a conceptual diagram illustrating the operation of a conventional electron beam lithography apparatus, and illustrates an example of variable shape electron beam lithography apparatuses.
In a first aperture 320, a rectangular opening 321 for producing an electron beam 300 is formed. In addition, a variable shaping aperture 331 for shaping the electron beam 300 passed through the opening 321 of the first aperture 320 into a desired rectangular shape is formed in a second aperture 330.
A sample 301 is placed on a stage that is continuously movable in a predetermined direction (for example, the X direction). The electron beam 300 emitted from an electron gun 310 and passed through the opening 321 of the first aperture 320 is deflected by the deflector and passed through a portion of the variable shaping aperture 331 of the second aperture 330 to irradiate the sample 301. That is, the electron beam 300 capable of passing through both the opening 321 of the first aperture 320 as well as the variable shaping aperture 331 of the second aperture 330 is formed, for example, into a rectangular shape, and, as a result, a rectangular shape is rendered on the drawing region (lithography region) of the sample 301. Such a method of rendering an arbitrary shape by passing the electron beam 300 through both the opening 321 of the first aperture 320 and the variable shaping aperture 331 of the second aperture 330 is referred to as a variable shaping method.
Together with the recent miniaturization of circuit patterns, there is a demand for improvement in the resolution of photolithography. One method to cope with this demand is a phase-shifting method in which photolithography is performed using a phase shifting mask. The above-described electron beam lithography apparatus can be used, for example, to manufacture a phase shifting mask (PSM) substrate for a phase shifting mask. In this case, an example of the sample 301 is a substrate to be processed for manufacturing a PSM substrate, and includes, for example, a glass substrate and one or more layers formed on the glass substrate.
As the phase shifting mask requires both a shading layer pattern and a half-tone layer pattern, the alignment (alignment accuracy) when superimposing these two patterns may become problematic. For example, a method is employed in which when a first layer pattern is formed, alignment marks are created on the shading layer and the half-tone layer, and when a second layer pattern is formed, the drawing position of the second layer pattern is adjusted based on the position of the alignment marks.
At this time, as it is difficult to arrange the alignment marks within the actual pattern (main pattern) of the first layer, it is generally arranged around the main pattern. In this way, the alignment marks are often arranged in the vicinity of or outside the boundary location of the lithography accuracy compensation region of the substrate (substrate to be processed). Therefore, there is a high probability that the positional accuracy of the alignment marks is inferior in comparison to those of the main pattern.